Cardiopulmonary resuscitation (CPR) is a well known and valuable method of first aid. CPR is used to resuscitate people who have suffered from cardiac arrest after heart attack, electric shock, chest injury and many other causes. During cardiac arrest, the heart stops pumping blood, and a person suffering cardiac arrest will soon suffer brain damage from lack of blood supply to the brain. Thus, CPR requires repetitive chest compression to squeeze the heart and the thoracic cavity to pump blood through the body. Very often, the victim is not breathing, and mouth to mouth artificial respiration or a bag valve mask is used to supply air to the lungs while the chest compression pumps blood through the body. The methods of providing oxygenated airflow to the lungs are referred to as ventilation.
It has been widely noted that CPR and chest compression can save cardiac arrest victims, especially when applied immediately after cardiac arrest. Chest compression requires that the person providing chest compression repetitively push down on the sternum of the victim at 80–100 compressions per minute. CPR and closed chest compression can be used anywhere, wherever the cardiac arrest victim is stricken. In the field, away from the hospital, CPR may be accomplished by ill-trained by-standers or highly trained paramedics and ambulance personnel.
When a first aid provider performs chest compression well, blood flow in the body is typically about 25–30% of normal blood flow. This is enough blood flow to prevent brain damage. However, when chest compression is required for long periods of time, it is difficult if not impossible to maintain adequate compression of the heart and rib cage. Even experienced paramedics cannot maintain adequate chest compression for more than a few minutes. Hightower, et al., Decay In Quality Of Chest Compressions Over Time, 26 Ann. Emerg. Med. 300 (September 1995). Thus, long periods of CPR, when required, are not often successful at sustaining or reviving the victim. At the same time, it appears that, if chest compression could be adequately maintained, cardiac arrest victims could be sustained for extended periods of time. Occasional reports of extended CPR efforts (45–90 minutes) have been reported, with the victims eventually being saved by coronary bypass surgery. See Tovar, et al., Successful Myocardial Revascularization and Neurologic Recovery, 22 Texas Heart J. 271 (1995).
In efforts to provide better blood flow and increase the effectiveness of bystander resuscitation efforts, modifications of the basic CPR procedure have been proposed and used. Various devices and methods described below are proposed for use in a main operative activity of CPR, namely repetitive compression of the thoracic cavity.
The device shown in Barkalow, Cardiopulmonary resuscitator Massager Pad, U.S. Pat. No. 4,570,615 (Feb. 18, 1986), the commercially available Thumper device, and other such devices, provide continuous automatic closed chest compression. Barkalow and others provide a piston which is placed over the chest cavity and supported by an arrangement of beams. The piston is placed over the sternum of a patient and set to repeatedly push downward on the chest under pneumatic power. The victim must first be installed into the device, and the height and stroke length of the piston must be adjusted for the patient before use, leading to delay in chest compression. Other analogous devices provide for hand operated piston action on the sternum. Everette, External Cardiac Compression Device, U.S. Pat. No. 5,257,619 (Nov. 2, 1993), for example, provides a simple chest pad mounted on a pivoting arm supported over a patient, which can be used to compress the chest by pushing down in the pivoting arm. These devices are not clinically more successful than manual chest compression. See Taylor, et al., External Cardiac Compression, A Randomized Comparison of Mechanical and Manual Techniques, 240 JAMA 644 (August 1978). Other devices for mechanical compression of the chest provide a compressing piston which is secured in place over the sternum via vests or straps around the chest. Woudenberg, Cardiopulmonary Resuscitator, U.S. Pat. No. 4,664,098 (May 12, 1987) shows such a device which is powered with an air cylinder. Waide, et al., External Cardiac Massage Device, U.S. Pat. No. 5,399,148 (Mar. 21, 1995) shows another such device which is manually operated.
Lach, et al., Resuscitation Method and Apparatus, U.S. Pat. No. 4,770,164 (Sep. 13, 1988) proposed compression of the chest with wide band and chocks on either side of the back, applying a side-to-side clasping action on the chest to compress the chest. Kelly, et al., Chest Compression Apparatus for Cardiac Arrest, U.S. Pat. No. 5,738,637 (U.S. Pat. No. 5,738,673) proposed compression of the chest using a wide band repeatedly tightened about the chest with a lever assembly placed on the patients sternum and operated manually. The Kelly devices comprises a base which is placed over a central region of the chest, a belt which is wrapped around the patients chest and fastened at its opposite ends to the base, and a force converter connected to the base and the belt, and a manual actuator, so that the force converter converts the downward force on the manual actuators into chest compressing resultants directed toward the chest and directed tangentially to the chest. Although Kelly illustrates installation of defibrillation electrodes on the wide band, he does not suggest integrating use of the electrodes with use of the compression belt in any manner.
In another variation of such devices, a vest or belt designed for placement around the chest is provided with pneumatic bladders which are filled to exert compressive forces on the chest. Scarberry, Apparatus for Application of Pressure to a Human Body, U.S. Pat. No. 5,222,478 (Jun. 29, 1993) and Halperin, Cardiopulmonary Resuscitation and Assisted Circulation System, U.S. Pat. No. 4,928,674 (May 29, 1990) show examples of such devices. Halperin, for example, uses a vest fitted with air bladders that are repeatedly inflated to compress the chest. The bladders are deflated by application of a vacuum. Cyclic inflation and deflation of the vest is accomplished with a complicated arrangement of two-way and three-way valves, connected to the bladders within the vest with large bore hoses.
Our own CPR devices use a compression belt around the chest of the patient which is repetitively tightened and relaxed through the action of a belt tightening spool powered by an electric motor. The motor is controlled by control system which times the compression cycles, limits the torque applied by the system (thereby limiting the power of the compression applied to the victim), provides for adjustment of the torque limit based on biological feedback from the patient, provides for respiration pauses, and controls the compression pattern through an assembly of clutches and/or brakes connecting the motor to the belt spool. Our devices have achieved high levels of blood flow in animal studies.
Abdominal binding is a technique used to enhance the effectiveness of the CPR chest compression. Abdominal binding is achieved by binding the stomach during chest compression to limit the waste of compressive force which is lost to deformation of the abdominal cavity caused by the compression of the chest. It also inhibits flow of blood into the lower extremities (and promotes bloodflow to the brain). Alferness, Manually-Actuable CPR apparatus, U.S. Pat. No. 4,349,015 (Sep. 14, 1982) provides for abdominal restraint during the compression cycle with a bladder that is filled during compression. Counterpulsion is a method in which slight pressure is applied to the abdomen in between each chest compression. A manual device for counterpulsion is shown in Shock, et al., Active Compression/Decompression Device for Cardiopulmonary Resuscitation, U.S. Pat. No. 5,630,789 (May 20, 1997). This device is like a seesaw mounted over the chest with a contact cup on each end of the seesaw. One end of the seesaw is mounted over the chest, and the other end is mounted over the abdomen, and the device is operated by rocking back and forth, alternately applying downward force on each end.
Electroventilation is the process of ventilating a patient by electrically stimulating the nerves that control the muscles used for respiration. It is proposed for use in patients that have been paralyzed such that the normal motor impulses transmitted to the diaphragm are not transmitted. Geddes, Demand Electroventilator, U.S. Pat. No. 4,827,935 (May 9, 1989) illustrates the operation of an electroventilator. He illustrates placement of two electrodes on the chest (one on either side), and application of electrical stimulus through the electrodes to stimulate the nerves responsible for triggering the muscles used in respiration. Geddes system provided for smooth inspiration, which was an improvement over the sharp gasping action caused by earlier electroventilation systems. The nerves identified by Geddes are the phrenic nerve, which controls the diaphragm, and the intercostal nerves which control the intercostal muscles (muscles between the ribs).